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Appendix IV.

959

between the plates is made up of 4 parts of sulphuric acid, having
a specific gravity of 1*84, to 21 parts of distilled water, both by
measure, the acid being slowly added to the water and the mixture
allowed to cool.

Now, there are three kinds of winding in continuous current
dynamos: (i) series wound, where the full armature current is

Zr.1

r2-s

carried round the magnets to excite them, and then to the mains,
all in * series;' (2) shunt wound, where a portion only of the
armature current is used to excite the magnets, carried in a small
bye-pass wire or shunt; (3) compound wound, where both
methods are adopted simultaneously. The shunt-wound dynamo
is alone suitable forcharging accumulators, except the excitation
be caused by a separate small dynamo. When all is ready, the
dynamo is run up to speed till the volts are properly adjusted,
and only then is the circuit closed with the cells, The charging
current should not exceed '026 ampferes per square inch plate of
surface, and there should be a constant pressure whose volts =